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Potato crops are generally sensitive to drought. Even a short period of water shortage can affect tuber production and quality. However, field potato crops undergoing mild water deficit conditions may acclimate to subsequent severe water deficits. While responses may be both acclimation and genotype-dependent, few studies have examined whole plant physiological factors leading to enhanced drought stress resistance. Identification of these key factors may increase selection efficiency in breeding programs. This study examined the effects of drought acclimation on drought stress resistance in three potato genotypes [‘Fv12246-6’ (Fv), ‘Vigor’ (V) and ‘Russet Burbank’ (RB)] in a low relative humidity greenhouse. Non-Acclimated and Non-Stressed (NA), Drought Acclimated and Drought Stressed (DAS) and Non-Acclimated and Drought Stressed (NAS) treatments were applied. Tuber yield and number were genetically determined and acclimation had no effect on increasing these components under drought stress. However, water conservation mechanisms based on leaf and stem characteristics were both genotype and treatment-dependent. When leaves were drought stressed while attached to the stem, genotype V and RB maintained a higher percentage of leaf water content (%LWC) than Fv, likely from the greater water stored in their stems that may have been delivered through continued leaf transpiration. Acclimation induced a thicker leaf cuticular layer and partially open stomata under drought stress in both RB and Fv. Nevertheless, Fv was the most drought sensitive potato genotype, displaying the highest degree of leaf wilting and lowest %LWC under drought stress. The observed drought stress-induced smaller stomatal size in Fv did not confer greater resistance. In addition, Fv displayed the lowest percentage shoot water content (%SWC) and slowest recovery time after drought stress. RB underwent the fastest recovery from drought stress, possibly due to its equivalent xylem to pith ratio which might have enhanced greater water uptake in RB than in V and Fv. Finally, compared to application of drought stress directly (NAS), a pre-treatment of drought acclimation cycles followed by drought stress (DAS) reduced leaf wilting, induced thicker cuticular layer and more open stomata under stress. Without a DAS approach, potentially key drought stress resistance mechanisms will be missed. The role of the stem as a potential water reservoir to adapt against drought stress should be examined to further identify key elements for drought stress survival and recovery at the level of the potato whole plant.

Carp [Cyprinus carpio) were acclimated to 8±1 C, 16±1.5 C and 26±1 C. Dark adapted retinas were isolated and light induced responses of HI horizontal cells recorded. The dynamic range of these cells was affected by temperature, showing a decrease on heating or cooling from an optimum temperature. The effect of acclimation was to shift this optimum in an adaptive manner. A move from 16 C to 8 C resulted in ~44% acclimation, while a move from 16 C to 26 C resulted in ~67% acclimation. The rates of change of membrane potential and latency of the response also showed adaptive changes on acclimation. Isolated horizontal cells were voltage clamped using the whole cell patch clamp technique. The current-voltage (I-V) relationship of the prominent anomalous rectifier current was displaced by changes in the extracellular potassium concentration and was blocked by Ba(^2+) or Rb(^+). Its amplitude did not appear to be affected by thermal acclimation. A pharmacologically isolated sustained Ca(^2+) current, with an I-V relationship characteristic of an L-type current, also showed no apparent thermal acclimation. The ratiometric calcium indicator Fura-2 was used to measure the intracellular calcium concentration in isolated horizontal cells. The intracellular calcium concentration rose on depolarization of the cells, in an extracellular calcium concentration dependent manner. This increase was blocked by various metal ions with varying sensitivities: La(^3+)>Cd(^2+)>Cu(^2+)>Co≥Ni(^2+). The rate of change of intracellular calcium concentration was increased by increased temperature, but did not appear to be affected by thermal acclimation. Sustained depolarizations (up to 15 minutes) resulted in sustained elevations in intracellular calcium concentration proportional to the degree of depolarization. Possible mechanisms underlying the long and short term effects of temperature on the horizontal cell responses are discussed. The sustained calcium current and the intracellular calcium concentration changes are disscused in terms of the potential roles of this current and the significance of the subsequent intracellular calcium concentration changes.

Many biotypes of the northem-hemisphere Arctic-Alpine grass Poa alpina L. reproduce asexually via prolification of the spikelet axis to produce dehiscing shoots. Although such pseudoviviparous plantlets are capable of photosynthesis, the source-sink characteristics of these synflorescence systems are unknown, including the degree to which plantlets are capable of providing for their own carbon requirements, or contributing to parental sinks. An initial anatomical investigation of the culm revealed that transpiration flow, as delimited by Lucifer Yellow tracer dye, was maintained despite advanced senescence (as evidenced by loss of chlorophyll and chloroplasts), with plantlet leaves driving transpiration flow. Transpiration flow was not hindered by cavitation or tylosis in older culms, the low frequencies of these processes being bypassed via nodal plexi. Despite this, water content of plantlets declined over time and visual indications of water stress became apparent, suggesting that water supply via the determinate culm was not sufficient for the increasing transpirational demand of indeterminate plantlets. Photosynthetic rates within the paracladial zone, as determined by infrared gas analysis (IRGA), exceeded respiratory rates by 3-4 fold, indicating that plantlets were sources of carbon. 14C tracer studies determined that the paracladial zone was not only as efficient at fixing carbon as the youngest fully expanded leaf, but that both organs exported carbon basipetally (c.f acropetal export from this leaf in seminiferous grasses). Distal plantlets fixed approx. 20% more 14C than proximal plantlets, by virtue of greater dry weight. Manipulative growth analysis of the paracladial zone suggests the operation of a system of apical dominance, with distal plantlets becoming dominant over proximal plantlets. At dehiscence, distal plantlets were more likely to become established, and possessed relative growth rates more than ten times those of proximal plantlets. Paracladial heterogeneity was also apparent as an increased proportion of aborted spikelets on proximal paracladia. Data indicate that this abortion was, at least in part, a result of constraint imposed by the pseudostem on the developing synflorescence. When grown in conditions of differing resource availability (altered nutrient supply and atmospheric C02 concentration), low nutrient availability in concert with elevated C02 concentration induced particularly low photosynthetic nitrogen and phosphorus use efficiencies in both parent and plantlet tissues. This occurred in concert with acclimatory loss of photosynthetic capacity leading to a decreased reproductive response of the plant; a product of the number of tillers in flower and the subsequent growth of attached plantlets. lt is predicted that in future climatic conditions Poa alpina will decline in habitats that include species which exhibit less acclimatory loss, no change, or an increase in photosynthetic capacity. These experiments also rule out resource availability as a cause of heterogeneity within the paracladial zone. A direct study of the phytohormonal characteristics of the pseudoviviparous system is therefore proposed in order to elucidate the mechanism of control within the paracladial zone.

<p> The procedures used to acclimate activated sludges for design criteria were reviewed. Experiments were performed to determine if cultures could be developed with the same characteristics as activated sludge from an actual treatment plant. Acclimation studies were performed with three refinery wastes. The resultant mixed cultures were compared, using removal rates, with activated sludge mixed cultures from the refinery's waste treatment plants. Soluble organic carbon was monitored for the removal rate curves. An acclimation procedure is proposed to be used in design studies so that a designer can place confidence limits on design data obtained from the batch reactor studies.</p> / Thesis / Master of Engineering (MEngr)

Although it has long been recognized that physiological acclimation of photosynthesis and respiration can occur in plants exposed to changing environmental conditions (e.g. light, temperature or stress), the extent of acclimation in different tissues (i.e. pre-existing and new foliage) however, has not received much attention until recently. Furthermore, few studies have investigated the extent of photosynthetic and respiratory acclimation under natural conditions, where air temperatures vary diurnally and seasonally. In this study, the effects of variations in temperature on respiratory CO2 loss and photosynthetic carbon assimilation were examined under both controlled and natural environments. The purpose of the investigations described in this thesis was to identify the effects acclimation would have on two key metabolic processes in plants exposed to temperature change, with emphasis also placed on the role of nutrition (nitrogen) and respiratory enzymatic characteristics on the potential for acclimation in two contrasting tree species, Pinus radiata and Populus deltoides. Controlled-environment studies (Chapter 2 and 3) established that rates of foliar respiration are sensitive to short-term changes in temperature (increasing exponentially with temperature) but in the longer-term (days to weeks), foliar respiration acclimates to temperature change. As a result, rates of dark respiration measured at any given temperature are higher in cold-acclimated and lower in warm-acclimated plants than would be predicted from an instantaneous response. Acclimation in new foliage (formed under the new temperature environment) was found to result in respiratory homeostasis (i.e. constant rates of foliar respiration following long-term changes in temperature, when respiration is measured at the prevailing growth temperature). Available evidence suggests that substantial adjustments in foliar respiration tend to be developmentally dependent. This may in part explain why respiratory homeostasis was only observed in new but not in pre-existing tissues. Step changes in temperature (cold and warm transfers) resulted in significant changes in photosynthetic capacity. However, in stark contrast to the findings of respiration, there was little evidence for photosynthetic acclimation to temperature change. The results obtained from field studies (Chapter 4) show that in the long-term over a full year, dark respiration rates in both tree species were insensitive to temperature but photosynthesis retained its sensitivity, increasing with increasing temperature. Respiration in both species showed a significant downregulation during spring and summer and increases in respiratory capacity were observed in autumn and winter. Thermal acclimation of respiration was associated with a change in the concentration of soluble sugars. Hence, acclimation of dark respiration under a naturally changing environment is characterized by changes in the temperature sensitivity and apparent capacity of the respiratory apparatus. The results from controlled and natural-environment studies were used to drive a leaflevel model (which accounted for dark respiratory acclimation) with the aim of forecasting the overall impact of responses of photosynthesis and respiration in the long term (Chapter 5). Modellers utilise the temperature responses of photosynthesis and respiration to parameterize carbon exchange models but often ignore acclimation and use only instantaneous responses to drive such models. The studies here have shown that this can result in erroneous estimates of carbon exchange as strong respiratory acclimation occurs over longer periods of temperature change. For example, it was found here that the failure to factor for dark respiratory acclimation resulted in the underestimation of carbon losses by foliar respiration during cooler months and an overestimation during warmer months - such discrepancies are likely to have an important impact on determinations of the carbon economy of forests and ecosystems. The overall results substantiate the conclusion that understanding the effect of variations in temperature on rates of carbon loss by plant respiration is a prerequisite for predicting estimates of atmospheric CO2 release in a changing global environment. It has been shown here that within a moderate range of temperatures, rate of carbon uptake by photosynthesis exceeds the rate of carbon loss by plant respiration in response to warming as a result of strong respiratory acclimation to temperature change. This has strong implications for models which fail to account for acclimation of respiration. At present, respiration is assumed to increase with increasing temperatures. This erroneous assumption supports conclusions linking warming to the reinforcement of the greenhouse effect.